Braun tube for producing television images rich in contrast



Aug. 24, 1937.

M. VON ARDENNE Y 1 2,090,922 I BRAUN TUBE FOR PRODUCING TELEVISIONIMAGES RICH IN CONTRAST Filed Oct. 18, 1935 Z7nren/or,

WWW ma Patented Aug. 24, 1937 BRAUN TUBE ron PRODUCING TELEVISION IMAGESRICH IN CONTRAST Manfred yon Ardenne, Berlin, Germany.

Application October 18, 1933, Serial No. 694,138 In Germany November 21,1932 8 Claims.

This invention relates to envelopes for Braun tubes for producingtelevision images rich in contrast.

Experiments have shown that the maximum range of contrast which iscapable of being obtained with.Braun tubes having envelopes oi the knownkind is considerably limited by the purely optical nature of theseenvelopes. There occurs on the inner wall of the bulb in the case ofthese 10 tubes a multiple reflection of the fluorescent light,

which results in the fact that a certain proportion again passes to thefluorescent screen in the form of secondary light. This effect isapparent to a particularly high degree in connec- 5 tion with tubes theenvelopes of which are metalcoated on the exterior, as in these there isa practically complete reflection of the light. The deficiency inquestion is particularly disturbing in the arse of large extent ofmovement of the beam of light and large fluorescent screens, and moreparticularly also in the case of tubes having bulbs with wide angle ofopening.

The object of the invention is an envelope for Braun tubes the entirewall of which, with the exception of the fluorescent screen, isconstructed in such fashion that a reflection is unable to take place atthe same in the interior of the bulb. It is possible for this purpose toblacken the inside of the wall of the bulb, for example by spraying ongraphite or finely divided soot. A

coating of this nature has been found to be adequately vacuum-proof, andis relatively simple to produce, as the application and the subsequentdrying requires only a very short time. Practically the same effect maybe obtained if J the darkening layer is applied to the outside of theenvelope, for example in the form of an intermediate layer between thewall of the envelope and the metallic coating. In this manner theapplication of the metallic coating is at the same time considerablyfacilitated, as the same adheres to the layer of carbon much morereadily and to a much better degree than to the glass wall.

It is also possible to employ envelopes, which are made opaque, moreparticularly on the inside. The opacity as such considerably diminishesthe power of reflection of the envelope wall, and improves the adhesionof the light-absorbing layer which may possibly be applied.

Naturally it is also possible, in place of graphite or carbon, to employother suitable light-absorbent substances.

The matting operation, however, is preferably 55 performed, not with asand blast, but by the use of one .of the known chemical mattingprocesses. To avoid the so-called halo efiect frequently observed in thecase of Braun tubes and based on similar causes to the halo effectoccurring in connection with photographic plates, it is possible inaccordance with the invention to apply to the outside of the bottomportions of the envelope-to the inside of which there is secured theluminous screena coating composed of a,

substance, the refractive index of which is greater than the index ofrefraction of the glass. This coating with preference may be weaklycolored.

In the drawing a form of embodiment of the invention is illustrated byway of example. In the same I is the envelope having a neck portion, abulb portion and a bottom portion, the bottom portion having theluminous coating 2, a layer composed of light-absorbent material, forexample graphite or carbon 4, and the outer metallic coating 5. On theoutside of the bottom portion there may be provided an additionalcoating 3 of suitable thickness consisting of a material, the refractiveindex of which is greater than the index of refraction of the glass ofthe bulb.

The measure according to the invention prevents the formation ofsecondary light by reflection within the tube, and accordingly per mitsof the production of images rich in contrast.

I claim:

1. An envelope for B'raun tubes comprising a neck portion, a bulbportion and a bottom portion, all of said portions being combined toform one structural unit, said neck and said bulb portion eachconsisting of matted, dark glass, said bottom being substantiallytransparent and being provided at its side facing the inside of saidenvelope with a luminescent coating.

2. An envelope for Braun tubes comprising a neck portion, a bulb portionand a bottom, said neck and said bulb portion each having at the insidea surface of highly light absorbing properties and each being furnishedat the outside with a metallic coating, said bottom being substantiallytransparent and being provided at its side facing the inside of saidenvelope with a layer of a luminescent substance.

3. An envelope for Braun tubes comprising a neck portion, a bulbportion, and a bottom portion, all of said portions being combined toform one structural unit, said bottom being provided at its side facingthe inside of the envelope with a layer of a luminescent substance, saidbottom being substantially transparent and being furtially transparentmaterial, the refractive index of which is greater than the index ofrefraction of the glass of which said bottom consists;

4. An envelope for Braun tubes comprising a neck portion, a bulbportion, and a bottom portion, all of said portions being combined toform one structural unit, said bottom being provided at its side facingthe inside of the envelope with a layer of a luminescent substance, saidbottom being substantially transparent and being furnished at itsoutside with a coating of a substantially transparent material, therefractive index of which is greater than the index of refraction of theglass of which said bottom consists, the material of which the lastmentioned coating consists being slightly coloured. I 7

5. An envelope for Braun tubes comprising a neck portion, a bulbportion, and a bottom portion, each of said portions consisting ofglass, all of said portions being combined to form one structural unit,said neck and said bulb portion each having at the inside a coating ofhighly light absorbing properties, said bottom being provided at itsside facing the inside of the envelope with a layer of a luminiscentsubstance, said bottom being substantially transparent and beingfurnished at its outside with a coating of a substantially transparentmaterial, the refractive index of which is greater than the index ofrefraction of the glass of which said bottom consists.

6. Anenvelope ior Braun tubes comprising a neck portion, a bulb portion,and a bottom portion, all of said portions being combined to form onestructural unit, said neck and said bulb portion each consisting ofmatted, dark glass, said bottom being provided at its side facing theinside of the envelope with a layer of a luminescent substance, saidbottom being substantially transparent and being furnished at itsoutside with a coating of a substantially transparent material, therefractive index of which is greater than the index of refraction of theglass of which said bottom -consists.

7. An envelope for Braun tubes compising a neck portion, a bulb portion,and a bottom, said neck and said bulb portion each having at the outsidea non-metallic coating of highly light absorbing properties, said bottombeing substantially transparent and being provided at its side facingthe inside of said envelope with a layer of a luminescent substance.

8. An envelope for Braun tubes comprising a neck portion, a bulbportion, and a bottom, a non-metallic coating of highly light absorbingproperties on the outsides of both said neck and said bulb portions, ametallic coating on said coating of highly light absorbing properties,said bottom being substantially transparent and being provided at itsside facing the inside of said envelope with a layer of a luminescentsubstance.

MANFRED vox ARDENNE.

